Almost all test vehicles are equipped to test carriers' 4G networks for performance and coverage

Verizon Wireless has equipped almost all of its fleet of test vehicles with 4G (fourth-generation) devices to test all the major U.S. 4G networks for speed and coverage.

The carrier has about 100 such vehicles around the U.S., and testers drive about 1 million miles (1.6 million kilometers) per year while conducting ongoing network tests, said Tom Badger, director of network system performance. Verizon commercially launched its own 4G LTE (Long-Term Evolution) network last December, and it now covers more than 160 cities. Some Verizon trucks have already been testing 4G networks, but the carrier is now set to study those networks across the country, along with ongoing 3G testing.

Verizon's archrival, AT&T, started commercial service on its own LTE network in five cities just last month. MetroPCS began rolling out LTE last September. Though Verizon didn't weigh in on the heated issue of what qualifies as a 4G network, Badger said the trucks test 4G and 3G networks including those of AT&T, T-Mobile USA, Sprint Nextel, Clearwire (Sprint's 4G partner), MetroPCS and Cricket, depending on which operators offer service in the local market.

On the sidelines of the CTIA Wireless Enterprise & Applications trade show in San Diego on Wednesday, Verizon showed off a Chevrolet Tahoe truck used to test networks in the San Diego area and nearby Imperial Valley. There are five test vehicles in the Southern California region, stretching from Ventura in the north to Mexico in the south, Verizon said. Those vehicles travel about 7,400 miles (11,909 kilometers) each quarter, and along the way make the equivalent of 29,000 voice calls and 142,000 data calls.

Shawn Bowers, the Verizon technician who drives the Tahoe as a full-time tester, said he travels over state and interstate highways, on residential streets and through downtown areas evaluating network quality. The routes are determined by U.S. Census data. The truck is equipped with four-wheel drive because it is a standard vehicle used across the country by Verizon. The feature can help in areas with snow, Bowers said, adding that he hasn't had occasion to use it in the sunny southern territory he drives.

Verizon tests its own and other networks using a variety of phones and mobile data devices such as USB modems. The devices make voice and data calls over the air and are wired up to testing equipment in the back of the truck, which is controlled by a laptop PC. That PC, in turn, is run remotely from another laptop fixed next to the driver's seat. The driver, who works alone, sets up the tests and then starts driving around while they run. All tests are mobile except when the vehicle is stopped in traffic, he said.

Data devices are attached to the back windows of the vehicle, while phones are stored in metal boxes, isolated from one another to prevent interference. The phones reach the cellular network through special antennas on the roof of the truck. To correct for the performance boost that comes from using those antennas, there is a "compensator" that adjusts the signal downward, Badger said.

Verizon tests for ability to achieve a data connection, data throughput on downloads and uploads, dropped calls, and voice quality. It's looking for consistent performance and trying to identify areas where the network may need to be upgraded. The test for voice calls uses .wav files of standard spoken sentences stored on the laptop, which are sent through the phones as they call back to phones at Verizon facilities, where the calls can be analyzed.

Verizon doesn't use a recording of the well-known phrase from its long-running series of TV commercials in which an actor playing a tester asked "Can you hear me now?" Instead, it uses "Harvard sentences" designed specifically to test a selection of voice sounds. They include "March the soldiers past the next hill" and "Tuck the sheet under the edge of the mat."